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Cellular Digital Packet Data or CDPD refers to a wide-area mobile data service that utilizes the unused bandwidth generally utilized by the AMPS mobile phones between the 800 and 900 MHz in order to transfer the data. Speeds up to 19.2 k bit/s were possible. The service was discontinued in conjunction along with the retirement of parent AMPS service; it has been functionally substituted by the faster services like 1xRTT, EV-DO, and UMTS/HSPA.

Parity and Checksums: Noise and momentary electrical disturbances might cause data to be modified as it passes via a communications channel. When the receiver fails to notice this, the received message will be wrong, resultant in possibly severe conse